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Tread softly

THE EUROPEAN TREE FROG HAD a problem. The dense network of roads built to serve the people of the Zeeuws Vlaanderen region of the Netherlands had thoroughly carved up its habitat. Each of the shreds that remained held too few frogs to create a thriving population. The roads isolated the fragments so effectively that even purpose-built frog underpasses wouldn’t solve the problem. As a last resort, conservationists opted to create new habitats to compensate for those lost to road development – but where?

The plight of the European tree frog is a familiar one. Engineers around the world have grown accustomed to dealing with the environmental fallout from roads that accidentally block animals’ movement, disturb wetland drainage or act as a beachhead for invasion of alien species. But it would be far better if they could spot potential problems right at the beginning and build road networks that were intrinsically environmentally friendly.

Often that simply hasn’t happened, says Harvard landscape ecologist Richard Forman – largely because ecologists and road planners approach the problem differently. Ecologists study how organisms live and move across entire ecosystems and speak in terms of populations and dispersal patterns, while road planners and engineers take a much narrower view, typically focusing on what’s happening at the roadside itself. For instance, roads can alter streams hundreds of metres away, but road planners can easily overlook the problem if they look only at the bits of land immediately beside the roads. If only ecologists and engineers could find a shared language for talking about roads and their effect on the environment.